1. Field of the Invention
The present invention relates to synthetic resin moldings with a front and rear layer of different properties whereby the front layer bears a printed surface capable of backlighting (that is, capable of making the pictorial image or lettering printed thereupon look bright if light is shone from the rear of the product and when viewed from the front), and to a method for the manufacture thereof.
The present invention falls under the International Patent Classifications B29F, F10, B29D11/00, and B29D31/00.
2. Description of the Prior Art
It is common knowledge that backlighting products (that is, products capable of making the pictorial image or lettering printed thereupon look bright if light is shone from the rear of the product and when viewed from the front), are used in various panels including automobile instrument panels and front panels of audio products.
These products are manufactured by imparting a printed image on to a synthetic resin sheet and on to synthetic resin moldings.
When a printed image is imparted on to a synthetic resin sheet (hereinafter referred to as sheet by way of abbreviation), it is possible to manufacture a multiplicity of 30 or 40 products simultaneously if a sheet having a large surface area is employed. If, however, a printed image is imparted on to a synthetic resin molding (hereinafter referred to as molding by way of abbreviation), it is possible to manufacture only a very small number of a mere two or four simultaneously, thereby resulting in a low productivity.
Even if a multiplicity of moldings were printed simultaneously, it would, consequently, be extremely complicated and expensive to produce the holding jigs for securing these moldings. And, further, even if it were possible to produce high-accuracy holding jigs, the print surfaces of the multiplicity of moldings would have slightly different heights due to variations in the molded products so that it would not be possible to achieve high-quality products, and the operating result would be most likely to give a low production yield.
Furthermore, the printing of moldings is a laborious operation in view of the extensive product handling requirements so that it requires approximately double the number of operators than sheet printing does.
Moreover, if multi-color printing is applied, the moldings require repeated washing and handling to thoroughly remove dust and dirt particles from the surface so that some impact forces, minor though they may be individually, will be applied to the molding. Under the cumulative action of these frequently repeated impact forces, however, the moldings will, in the course of time, fracture, and protruding parts will break off.
For the printing of moldings it is essential that the print surface should be flat. Yet, even if the molding itself is flat, the holding jig tends to result in minor incurvation and sloping of the surface, thereby causing a reduction in product quality and thus a drop in the production yield.
Further, moldings are not always flat and will occasionally be found to have convexities or concavities on one or many of their surfaces.
Furthermore, certain parts may have convexities and concavities on their surfaces.
This renders the surface incapable of being printed, except by the special printing technique known as pad printing.
While printing by the pad printing method may produce surfaces that appear perfect on cursory inspection, it cannot meet the essential objective, since, with the use of backlighting, a process deemed necessary also for molding such as automobile instrument panels and audio products, and entailing that the printed pattern and lettering should stand out clearly against the light shone from the rear, the printed pattern and lettering that should stand out clearly will appear to be riddled with pinholes while the other (normally black background) parts are suffused with light resulting in a pattern similar to that of a star-speckled sky at night.
Apart from those printing techniques involving the direct application of print on to the molding, the following methods are available for providing a print surface to the molding.
One such method is known as the Simultranser System (in-mold technique). This is a fully integrated molding and printing system in which a transfer image foil is positioned inside the injection molding die and the image is transferred onto the molding in the molding process, so that the molding process and the transfer image application process are accomplished in a single operation.
The problem associated with this process, however, lies in the fact that since only the ink film layer printed on the film is transferred on to the molding during the molding process, the weld lines and gate marks generated on the molding cannot be concealed so that the product's appearance suffers.
Another such method is known as the heat transfer system, a process in which a printed area (pattern), that is, a pattern printed on a film, is heat-transferred on to a molding by means of a hot stamping device.